U.S. Pat. No. 4,000,066 (Dec. 28, 1976) broadly discusses two significant uses of a panel bed of granular material: (1) for filtering powdery matter from a liquid, the filtration being assisted by an accumulation of powdery matter deposits (filter cakes) upon fluid-entry faces of the granular material; (2) for countercurrent contacting of the granular material with a liquid. See also “Granular-bed filtration assisted by filter-cake formation: 5. Treating a liquid in a panel bed with pulseback renewal of liquid-entry granular-bed faces,” by J.-S. Yang, D. R. Whitmire, and A. M. Squires, Powder Technology, vol. 155, pp. 134-138, 2005.
The referenced patent discloses means for renewing liquid-entry faces of a panel bed of a granular material in which vertically disposed louvers (resembling slats of a Venetian blind) support the material: i.e., to provide a “reverse” surge flow of liquid toward the liquid-entry faces (a “pulseback”). This surge flow produces a body movement of the granular material toward the faces, spilling moieties of the material from the faces and concomitantly exposing previously underlying material, thereby renewing the faces.